The secondary compression plate seal ″U" is a rim mounted system suitable for floating roof tanks of all sizes storing all grades of crude and refined products. It is designed to be installed whilst the tank is still in service. The seal incorporates a compression plate, synthetic rubber wiper and vapour barrier membrane. The compression plate can be made from either galvanised steel or stainless steel. The vapour barrier membrane is normally manufactured from polyurethane-coated nylon fabric with very low vapour permeability properties.